Field of the Invention
The present invention relates to a control device for a link actuator that is used in equipment such as, for example, medical device or industrial device that requires a precise and wide operating range.
Description of Related Art
One example of working device equipped with a parallel link mechanism is disclosed in the Patent Document 1 listed below. Since the parallel link mechanism used in this working device has a plurality of links each having such a small operating range that the link length need be increased if the operating range of a travelling plate is desired to be expanded. Also, if the link length is increased, reduction in rigidity of the mechanism in its entirety results in. For this reason, there has been recognized such a problem that the weight of a tool mounted on the travelling plate, that is, the weight capacity of the travelling plate is limited to a small one.
In order to alleviate the foregoing problem, a link actuator provided with three or more sets of link mechanisms in quadric crank chain has been suggested (in, for example, the patent documents 2 and 3 listed below). According to the suggested link actuator, the operation within a precise and wide operating range is possible while it is compact in size.
FIGS. 22 and 23 of the accompanying drawings illustrate one example of the link actuator provided with three or more link mechanisms in trinodal crank chain. The illustrated link actuator 1 includes a proximal end side link hub 14, a distal end side link hub 15, and three link mechanisms 11, 12 and 13 each connecting those link hubs 14 and 15 together. Each of the link mechanisms 11, 12 and 13 is made up of a proximal side end link member 11a, 12a or 13a, a distal side end link member 11b, 12b or 13b and an intermediate link 11c, 12c or 13c, all cooperating to define a corresponding link mechanism in the trinodal crank chain comprised of four revolute pairs. It is to be noted that in FIGS. 22 and 23, the distal side end link member 13a is not illustrated for the sake of clarity. Also, the distal side end link members 11a, 12a and 13a are hereinafter referred to as arms 11a, 12a and 13a, respectively.
According to the above described link actuator of the structure discussed above, a proximal end side link hub 14, a distal end side link hub 15 and three set of link mechanisms 11, 12 and 13 cooperate with each other to form a mechanism of two degree of freedom in which the distal end side link hub 15 is movable relative to the distal end side link hub 14 in two axial directions perpendicular to each other. This two degree of freedom mechanism, while compact in size, is capable of providing the distal end side link hub 15 with a large operating range. By way of example, the maximum bending angle between the center axis QA of the proximal end side link hub 14 and the center axis QB of the distal end side link hub 15 is about ±90 degree and the pivot angle φ of the distal end side link hub 15 relative to the proximal end side link hub 14 can be set to the range of 0 to 360 degree.